The invention relates to a multi-stage centrifugal pump assembly having a motor housing with a motor shaft which is rotatably mounted and which carries a rotor, and having a pump housing with a rotatably mounted pump shaft, on which impellers are arranged in a rotationally fixed manner, wherein the pump housing is fixedly connected to the motor housing, and the motor shaft is fixedly connected to the pump shaft, and the motor-side end of the pump shaft is fixed within a pocket hole at the pump-side end of the motor shaft, and having a bearing for the shaft mounting, which is arranged in a bearing carrier provided in the connection region of the housing.
Multi-stage centrifugal pump assemblies of this type, in their most varied of designs, are counted as belonging to the state of the art. In this context, the assemblies manufactured and marketed by the company Grundfos under the type description CH and respectively CHN, for example the assembly of the type CHN2-50 with a drive motor MG71 are referred to only by way of example. With regard to these multi-stage centrifugal pumps, it is in particular the case of those whose shaft is arranged in a lying manner, which means to say horizontally with the usual alignment.
The pump assemblies of the above mentioned construction series have proven their worth in practice. They comprise a motor housing with a motor shaft rotatably mounted therein, which carries a rotor, as well as a pump housing with a rotatably mounted pump shaft, on which several impellers are arranged in a rotationally fixed manner. The motor housing is firmly connected to the pump housing and typically comprises a common component, the bearing carrier, which radially supports the pump-side end of the motor shaft, and the motor-side end of the motor shaft, which is incorporated in this region. Thereby, the motor-side end of the pump shaft is fixed within a pocket hole on the pump-side end of the motor shaft, and specifically by way of a press fit, which is usually effected by way of thermal joining, which means by way of joining after heating the motor shaft and cooling the pump shaft and/or by way of mustering suitably high forces in the axis direction of the shafts. This basically does not represent a problem, but has the disadvantage that the shaft connection must typically be effected before the finishing assembly of the motor, since the separate heating of the motor shaft is otherwise not possible. Moreover, the motor is usually not designed for mustering such high axial forces, as are required for the joining of a press fit. Thus, on motor manufacture, one must already ascertain which pump, that is to say which shaft, is applied for which number of impellers. Moreover, the axial construction length of this known design in the region of the bearing/shaft connection is comparatively large, since the press fit is arranged outside the bearing region, in order not to negatively influence this.